Device for heating nonmetallic materials,more particularly food-stuffs,by microwave energy in a cavity resonator



April 1, 1969 H. A. PUSCHNER 3,436,507

DEVICE FOR HEATING NONMETALLIC MATERIALS, MORE PARTICULARLY FOODSTUFF-SBY MICROWAVE ENERGY IN A CAVITY RESONATOR Filed June 10. 1966 9%WAMUnited States Patent US. Cl. 219-1055 5 Claims ABSTRACT OF THEDISCLOSURE A microwave oven is fed from the top through an inputcoupling system connecting the heating chamber with the microwavegenerator. A sealed stirrer is in the heating chamber supported forrotation coaxially to the input coupling system and has a primaryradiator and an array of secondary radiators so that rotation of thestirrer keeps the field in the oven essentially uniform.

The invention relates to a device for heating nonmetallic materials,more particularly foodstufis, by microwave energy in a cavity resonator.

In such devices the cavity resonator serves as the heating chamber and acoupling system is provided which connects the heating chamber with themicrowave generator, an oscillation-type converter being provided whichrotates in the heating chamber. Hitherto, the converter has beenprovided apart from the coupling system, on the assumption that by thisan especially uniform field distribution and uniform heating of thematerial would be achieved. Practice has shown however that with such anarrangement, undesirably high field strength differences occur in theheating chamber which cause nonuniform heating and necessitatecorrespondingly longer heating times in order to bring the entirematerial to the desired final temperature.

The present invention is based on the consideration that an arrangementof the converter apart from the coupling system results in an operativemechanism which is difiicult to supervise and is independent of theotherwise usual geometric relationships. Starting from thisconsideration, in a device constructed according to the invention, theconverter is arranged to rotate coaxially to the input coupling system.As a result of this, by suitably distributing the secondary radiators ofthe oscillation-type converter relative to the coupling system, it ispossible to produce a desired field distribution and to achieveexcitation of only such oscillation modes which result insuperimpositions of the desired field distribution in the chamber.

A particularly advantageous utilisation of the coaxial arrangement ofthe input coupling system and oscillationtype converter is achieved ifthe wave coming from the coaxial input is coupled to theoscillation-type converter through a coaxial conical transition. Theoscillation-type converter can consist of a number of secondaryradiators and the polarisation of the secondary radiators can bedistributed over all three space coordinates of the cavity resonator. I1

3,436,507 Patented Apr. 1, 1969 In order to make the invention clearlyunderstood, reference will now be made to the accompanying diagrammaticdrawings which are given by way of example and in which:

FIG. 1 illustrates a cavity resonator with an input coupling system andan oscillation-type converter; and

FIG. 2 is a plan view of FIG. 1.

The illustrated device comprises a heating chamber 1 in which foodstuffto be heated can be placed. The heating chamber has a door 2 at itsfront side.

The heating chamber 1 is formed as a cavity resonator for the microwaveenergy which is used, and for this purpose is provided with a wall 2which consists of metal or which is provided with a metallic cladding.In the centre of the top, as an input coupling system, a coaxial linewith an outer conductor 4 and an inner conductor 5 is provided. In thechamber 1, a conical transition 6 of metal is connected to the innerconductor 5, its base surface carrying a circular plate 7 with aplurality of secondary radiators '8 which are in the form of narrowmetal strips. The plate 7 which consists of nonmetallic material, withthe metal transition cone 6 connected to the inner conductor 5, servesas an oscillation-type converter and is arranged for rotation.

I claim:

1. A device for heating nonmetallic materials, such as foodstuffs, bymicrowave energy, comprising a cavity resonator serving as a heatingchamber, a microwave generator, an input coupling system connecting theheating chamber with the microwave generator, and field stirring meansrotatably disposed in the heating chamber, means for supporting saidfield stirring means for rotation coaxially to the said input couplingsystem, said field stirring means including a primary radiator and anarray of secondary radiators.

2. A device according to claim 1, wherein said primary radiator includesa conical transition member disposed coaxially to the input couplingsystem and arranged for coupling a wave from the input coupling systemto said primary and secondary radiators.

3. A device according to claim 1, wherein the secondary radiators arecarried by a nonmetallic and circular plate carried by said conicaltransmission memher.

4. A device according to claim 1, wherein the polarisation of thesecondary radiators is distributed over all three space coordinates ofthe cavity resonator.

5. A device according to claim 3, wherein the secondary radiators are inthe form of narrow metal strips.

References Cited UNITED STATES PATENTS 2,748,239 5/1956 Long et a1219-10.55 2,961,520 11/1960 Long 219--10.55 3,364,332 1/1968 Sven-OlovReftmark FOREIGN PATENTS 1,482,777 5/1967 France.

RICHARD M. WOOD, Primary Examiner. L. H. BENDER, Assistant Examiner.

